The following paragraphs are not an admission that any of the information below is common general knowledge or citable as prior art.
Selenium is an essential trace element, but becomes toxic at very low concentrations. Selenium accumulates in the bodies of plants and fish that live in selenium-contaminated water and in the bodies of wildlife and people that eat those plants and fish. In people, elevated selenium concentrations may cause neurological damage and hair and nail loss.
Selenium has been treated in biological reactors, for example as described in U.S. Pat. No. 6,183,644 and International Publication Number WO 2007/012181, and as used in ABMet™ reactors sold by the GE Water and Process Technologies. In such reactors, dissolved selenium is removed from contaminated water by treating the water in a reactor containing selected endemic and other selenium reducing organisms. Microbes may be isolated from the specific water or imported from other selenium contaminated water. The microbes are then screened for ability to reduce selenium under the site specific environmental conditions. The selected microbes are optimized for selenium reduction, then established in a high density biofilm within a reactor. The selenium contaminated water is passed through the reactor with optimized nutrient mix added as needed. The elemental selenium is precipitated and removed from the water. U.S. Pat. No. 6,183,644 is incorporated herein by reference.
U.S. Publication No. 2010/0300963 describes an apparatus and process for treating flue gas desulfurization blow down water or other wastewaters having selenium. The process has steps of one or more of aerobic treatment to remove chemical oxygen demand and nitrify a waste stream, anoxic treatment to denitrify a waste stream, anoxic treatment to remove selenium and anaerobic treatment to remove heavy metals and sulphur. The process may further include one or more of (a) membrane separation of the waste stream upstream of the anoxic digestion to remove selenium, (b) dilution upstream of the biological treatment step, (c) physical/chemical pretreatment upstream of the biological process or dilution step to remove total suspended solids (TSS) and soften the waste stream, or (d) ammonia stripping upstream of the biological treatment step or dilution step. One or more of these processes may be provided in a membrane bioreactor or a fixed film reactor having a granular activated carbon (GAC) bed. U.S. Publication No. 2010/0300963 is incorporated herein by reference.